GB1559964A - Process for treating liquid steel intended in particular for manufacturing machine wire - Google Patents

Description

PATENT SPECIFICATION

( 21) Application No 11932/78 ( 22) Filed 22 March 1978 ( 31) Convention Application No 7 709 737 ( 32) Filed 31 March 1977 in ( 33) France (FR) ( 44) Complete Specification published 30 Jan 1980 ( 51) INT CL 3 C 21 C 7/06 ( 52) Index at acceptance C 7 D 3 G 1 B 3 G 1 D 3 G 1 E 3 G 33 G 53 G 7 A 3 G 7 G 3 G 7 K 3 G 7 L ( 11) 1 559 964 ( 54) IMPROVEMENTS IN OR RELATING TO A PROCESS FOR TREATING LIQUID STEEL INTENDED IN PARTICULAR FOR MANUFACTURING MACHINE WIRE ( 71) We, UNION SIDERURGIQUE DU NORD ET DE L'EST DE LA FRANCE, a French Body Corporate of 14, rue d'Athenes, 75426 Paris Cedex 09, France, do hereby dedare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:The present invention relates to a process for treating liquid steel intended in particular for the manufacture of machine wire or rod which may be used in particular in the preparation of cables for tire carcasses or other like reinforcing elements.

The metal reinforcing elements for tires are produced from twisted cables comprising a plurality of fine wires obtained by a cold wiredrawing operation down to a very small diameter (to about 0 15 mm) of a hot-rolled machine wire or rod Bearing in mind the envisaged utilization, this machine wire must be produced in a grade of steel which must have the following characteristics:

homogeneous and precise chemical composition; minimum content of non-metallic inclusions; composition and structure of the nonmetallic inclusions which impart thereto good deformability properties in the cold state.

Heretofore, the steel employed for manufacturing a machine wire or rod was a steel produced by a conventional process in respect of which the sole important precautions concerned the property of the steel and the minimum incorporation of killing elements.

Now, the steel prepared in this way nonetheless comprises a large proportion of nonmetallic inclusions formed by the combination of the killing elements with the oxygen of the metal which results in a poor wiredrawing capability of the machine wire obtained.

Indeed, the inclusions constituted by these refractory minerals are hard and therefore but little deformable and result in rapid wear of the wiredrawing dies and fracture of the wire in the course of the final twisting operation owing to the heterogeneous distribution of these inclusions.

Thus, in order to minimize the killing elements to be added, currently-employed conventional processes are carried out in particular by degassing the steel as far as possible by the use of an installation for placing the pouring ladle containing the treated liquid steel under a vacuum However, such an installation is expensive in construction and.

operation and does not produce alone the desired results for obtaining machine wires.

Although it does not disclose a process for obtaining a machine wire, French Patent No.

1,235,699 teaches employing an agitation by means of an inert gas to achieve an improved deoxidation, but this process is also unsatisfactory in the application envisaged in the present invention.

An object of the present invention is to overcome these drawbacks by providing a process for producing a steel for a machine wire which has a homogeneous composition, much smaller amounts of inclusions and good cold deformability properties.

According to the invention, there is provided a process for treating liquid steel for manufacturing machine wire, comprising adding all or part of the manganese to an extramild steel, obtained after refining by any steel production process, directly in the steel production apparatus to obtain the desired manganese content, pouring the steel thus obtained into a first ladle or into another pouring apparatus and adding carbon to the liquid mass in the first ladle and pouring the steel obtained into a second ladle and adding a given amount of, first, silicon and then aluminium According to another feature of the invention, an element selected from calcium, barium and strontium may also be added at the same time as the silicon.

The three-stage process according to the invention therefore permits obtaining an 2 1,559,964 appropriate grade of the steel to produce the required qualities of the machine wire.

The addition of manganese to the steel in the production apparatus, which may be a furnace or converter, is achieved for example by means of ferro-manganese added in the proportion of 05-1 5 % by weight of Mn, calculated in the elementary form, so as to obtain a Mn content in the steel higher than 0 3 % and in particular 04-0 8 % This addition of Mn results in a beginning of a deoxidation and the Mn O which is partly incorporated in the slag is eliminated at the same time as the latter.

The metal treated with the manganese is then poured into a first pre-heated ladle or into another pouring apparatus (which may be, for example, a furnace).

Carbon, in a particularly appropriate form powdered graphite, is then added in this first ladle in a sufficient amount to continue the deoxidation of the steel and give the desired carbon content of the steel The carbon is added in the proportion of 0 1-1 0 % by weight Thus a part of the carbon added combines with the oxygen to form carbon monoxide which is eliminated in the gaseous form.

The carbon is introduced in the liquid mass by any means ensuring a homogeneous distribution of this element, for example in the form of a powder immersed in an inert gas such as argon directly introduced into the steel.

The amount of carbon added is such that a carbon content is obtained in the steel which is higher than 0 2 % by weight and preferably 0.6-0 8 % by weight.

Subsequent to this second stage, the liquid steel has already undergone two successive deoxidations, namely a first deoxidation by means of the manganese which was partly eliminated in the form of Mn O, and a second deoxidation by means of the carbon a part of which was eliminated in the gaseous form.

Consequently, a considerable deoxidation of the steel is achieved with a minimum amount of killing elements This reduction in the amount of the killing elements facilitates the obtainment of the desired properties since it reduces to a minimum the amount of inclusions which are necessarily present.

The steel obtained at the end of the second stage is then transferred to a second pouring ladle which is preferably preheated In this second ladle, the steel is subjected to a final deoxidation by the addition of given amounts of, first, silicon and then aluminium so as to obtain oxidized inclusions which correspond to the desired composition of these inclusions which have advantageous deformability properties.

The silicon is added first of all in the form of ferrosilicon or silicon alloy in the proportion of about 1-4 kg per metric ton of steel corresponding to an added amount, calculated in the form of elementary silicon, of 0 0060.26 % by weight, so as to obtain a silicon content in the steel of lower than 0 3 % The aluminium is then added in the proportion of 0.0005-0 010 %, calculated in the elementary form, so as to obtain a final aluminium content in the steel of less than 0 010 % by weight which generally corresponds to an addition of to 20 grams of aluminium per metric ton of steel.

The amounts of silicon and aluminium added must be determined at the moment of use in the particular steel employed by taking into account the manganese content already present, so as to bring the composition of the oxidized inclusions within the range of maximum plasticity of the given ternary diagram represented bv the crosshatched zone A of the accompanying Figure.

The process according to the invention permits achieving for the composition of the oxidized inclusions the maximum plasticity range which is particularly appropriate for obtaining the required deformability properties of the inclii'zons Now, this range can only be obtained by means of prior deoxidations which leave only a minimum amount of non-metallic inclusions, since they have been partly produced with the use of carbon and manganese.

According to another manner of carrying out the invention, a killing element selected from calcium, barium and strontium may also be employed as a final killing element in addition to the silicon and aluminium in the course of the treatment in the second ladle This element is then introduced at the same time as the silicon in the proportion of 0 0010.04 / by weight, calculated in the elementary form, relative to the steel The aluminium is then introduced after the addition of the silicon and the additional killing element.

In the case of the use of this additional killing element, the proportions of Si and Al added remain identical to those hereinbefore defined.

A preferred additional killing element is calcium which is introduced into the steel at the same time as the silicon in the form of silico-calcium.

It is essential in the process of the invention to take care that the steel in the second pouring ladle is maintained at a temperature distinctly higher than the beginning of the freezing (liquidus) of the considered steel composition, for example 50-70 C.

This result may be obtained by employing, for each of the two treating operations outside the production apparatus, ladles preheated to a temperature of at least 12000 C and provided with sliding nozzles.

EXAMPLE.

One manner of carrying out the process of the invention is summarized in the following Table I.

1,559,964 A steel produced in the converter is blasted until it reaches an extramild state and has the indicated initial characteristics.

TABLE I

Temperature Activity Content of Mn P S Si Al Steps of the treatment C 02 in ppm C% x 10-3 % x 10-3 % x 10-3 % Y 10-3 % 103 % x 10-, End of the blasting in the converter 1110 14 90 26 15 First stage in the converter After addition of 12,3 kg/t of ordinary Fe Mn carbide + lime + soda 1610 350 85 636 24 12 2nd stage Pouring into an intermediate ladle No I + recarburization by injection of 7,7 kg/t of graphite 1540 40 730 613 26 14 3rd stage Transfer to the ladle No 2 4 final deoxidation by addition of 3,0 kg/t of Fe Si 4 20 g/t of Al 1515 15 725 600 26 14 192 2 1 1 -h o In 0,11 t, 1,559,964 The process according to the invention therefore permits grading a steel intended for manufacturing a machine wire having improved wiredrawing properties Indeed, these properties are obtained owing to the presence of cold-deformable oxidized inclusions which are present in a minimum amount These results are obtained by a deoxidation of the steel which, achieved partly by elements, namely the manganese and the carbon, the products of combination of which with the oxygen are substantially completely eliminated before the final stage, is completed and terminated with elements such as silicon, aluminium, and possibly calcium, barium and strontium the addition of which may be adjusted to a minimum amount which corresponds to a maximum placticity range of the inclusions Thus, in the case of the use of Mn, Si and Al, this maximum plasticity range corresponds to the zone A of the ternary diagram AI O,-Si O,-Mn O in the accompanying Figure.

The killing conventionally carried out on steel by the addition of deoxidizing elements in one go did not permit obtaining this required particular composition and consequently the cold-deformability properties of the inclusions.

Although this feature is secondary, the steel may also be treated in caisson-ladles which enable the process to be carried out under a vacuum, such as for example those disclosed in the French patent application 70 00 579, possibly provided with stirring means, such as a bubbling of argon through a porous brick.

Claims (9)

WHAT WE CLAIM IS:-

1 A process for treating liquid steel for manufacturing machine wire comprising adding all or part of the manganese to an extra-mild steel, obtained after refining by any steel production process, directly in the steel production apparatus to obtain the desired manganese content, pouring the steel thus obtained into a first ladle or into another pouring apparatus and adding carbon to the liquid mass in the first ladle and pouring the steel obtained into a second ladle and adding a given amount of, first, silicon and then aluminium.

2 A process as claimed in claim 1, comprising adding in the steel 05-1 5 % by weight of manganese calculated in the elementary form.

3 A process as claimed in claim 1 or 2, comprising adding 0 1-1 0 % by weight of powdered carbon in the form of graphite.

4 A process as claimed in claim 1, 2 or 3, comprising adding in the steel 0 06-0 26 % of Si and 0 0005-0 01 % of Al calculated in the elementary form.

A process as claimed in any one of the preceding claims, wherein the various proportions of manganese, silicon and aluminium added provide a composition of the inclusions corresponding to the maximum plasticity range of the ternary diagram Si O,-Al,0,-Mn O represented by the zone A of the accompanying Figure.

6 A process as claimed in any one of the claims 1 to 5, further comprising adding with the silicon an additional killing element selected from calcium, barium and strontium.

7 A process as claimed in claim 6, wherein the additional killing element added is introduced in the steel in the proportion of 0 0010.04 % calculated in the elementary form.

8 A process as claimed in any one of the preceding claims, comprising employing preheated ladles provided with sliding nozzles so as to pour the steel into ingot moulds at a temperature which it at least 500 C higher than the temperature corresponding to the beginning of the freezing of the steel.

9 A process for treating liquid steel for manufacturing machine wire, substantially as hereinbefore described.

MARKS & CLERK, 7th Floor, Scottish Life House, Bridge Street, Manchester, M 3 3 DP.

Agents for the Applicants.

Printed for Her Majesty's Stationery Office by the Courier Press, Leamington Spa, 1980:

Published by the Patent Office, 25 Southampton Buildings, London, WC 2 A l AY, from which copies may be obtained.